Aflatoxin B1 is one of the most potent chemical carcinogens found in the human environment. This and other aflatoxins are common contaminants in agricultural products. Our previous studies have shown aflatoxin B1 and G1 can be converted by hamster and mouse liver homogenates to metabolites which are mutagenic in Neurospora. Our studies also showed that addition of the epoxide-hydrase inhibitor, 1,1,1-trichloropropane-2,3-oxide, to the test system increased ad-3 mutation frequency. Further studies using the ad-3 test system of Neurospora are carried out to determine whether 1) aflatoxins can be converted by rat liver homogenates to metabolites mutagenic in Neurospora, 2) more mutagenic metabolites are being converted from aflatoxin B1 than G1 by rat liver homogenate, 3) more mutagenic metabolites are being converted from aflatoxin G1 than by B1 by kidney homogenates of male rats, 4) kidney homogenates from female rats are failing to convert aflatoxin B1 and G1 to mutagenic metabolites, 5) NADPH is necessary for the conversion of aflatoxin to mutagenic metabolites and 6) pretreatment of mamals with phenobarbital increases the conversion capacity. BIBLIOGRAPHIC REFERENCE: Matzinger, P.K. and Ong, T.: Mutation induction of rodent liver microsomal metabolites of aflatoxin B1 and G1 in Neurospora crassa. Mutation Research 37: 27-32, 1976.